Transmission ??

[ETP]

I have a 99 430 with 70K. Car has been well maintained. Recently I accelerated hard from a stop. The engine pulled hard and rev freely to redline. the trans howerever seemed to stumble and refused to shift to the next gear.. eventually shifting just pass redline but only after you let off the pedal. It does this through 1,2,3 gear and then goes like a rocket in 4th. Under normal driving it shifts ok. I have reset the trans twice without any change. Fluid change was done at 60k. Fluid level is spot on. I don't know where to start looking for the problem